The continuous miniaturization of integrated circuit ("IC") dies has resulted in the cluster packaging of plural dies within single high density IC packages ("HDPs"). The die input/output ("I/O") leads are arrayed along the perimeter of the HDP to facilitate the electrical connection of the dies to external circuitry, such as that found on a printed circuit board ("PCB"). The HDP leads must be coated with solder, i.e., "tinned", in preparation for mounting on the PCB. After tinning, the HDP can be mounted to the surface of a PCB by melting the tinned solder onto copper pads on the PCB with infra red radiation.
It is known in the art to use mechanical means to hold HDPs in a fixture for tinning the leads in a wave soldering machine. The typical prior art fixtures include a base adapted to receive a plurality of HDPs positioned in a matrix array, and a clamping mechanism that secures the HDPs to the base. The fixture may be constructed of titanium or fluorocarbon polymer coated metal.
The base portion of these prior art fixtures is an orthogonal grid structure. The grid allows molten solder to flow through the structure and contact the top or "case" of the HDPs. Consequently, solder will adhere to HDPs with metallic cases, producing visual scrap or, by covering the part marking, render the HDP unidentifiable.
Similarly, the clamping mechanism of the prior art fixtures which utilize mechanical means to hold HDPs may interfere with the natural flow of solder in the wave soldering machine, in a phenomenon known as "shadowing." This shadowing may cause solder balls, uneven coating of solder, and failure of solder to adhere to the HDP leads.